Collaborative design often meets together experts of different domains. Such groups need to share a context but often limited this one is often limited to few elements as common language, common tools and a same goal (the design process). Our goal is to developing a shared context to make compatible different experts' viewpoints. Making context explicit and shared supposes some explanatory capability. In this paper, we point out how context and explanation are intertwined, and the need of a uniform representation of elements of reasoning and of contexts for offering a larger spectrum of explanation in a collaborative design.